Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,247	$ 2,305	$ 2,101
DB Pension Plans | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	242	21
DB Pension Plans | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	242	21
DB Pension Plans | U.S. government and agencies securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	4
DB Pension Plans | U.S. government and agencies securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	4
DB Pension Plans | Corporate debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	400	336
DB Pension Plans | Corporate debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	400	336
DB Pension Plans | State and municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	9
DB Pension Plans | State and municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	9
DB Pension Plans | Foreign corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35	31
DB Pension Plans | Foreign corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	35	31
DB Pension Plans | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	552	662
DB Pension Plans | Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	552	662
DB Pension Plans | Plan Assets Excluding Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,246	1,063
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	794	683
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	452	380
DB Pension Plans | Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,001	1,242
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,280	1,420	1,264
OPEB Plan | Consumers Energy Company
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,197	1,329	$ 1,184
OPEB Plan | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	36	16
OPEB Plan | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	36	16
OPEB Plan | U.S. government and agencies securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
OPEB Plan | U.S. government and agencies securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
OPEB Plan | Corporate debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	50
OPEB Plan | Corporate debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	50
OPEB Plan | State and municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
OPEB Plan | State and municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
OPEB Plan | Foreign corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	4
OPEB Plan | Foreign corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	4
OPEB Plan | Common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41	40
OPEB Plan | Common stocks | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41	40
OPEB Plan | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	594	647
OPEB Plan | Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	594	647
OPEB Plan | Plan Assets Excluding Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	734	759
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	671	703
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63	56
OPEB Plan | Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 546	$ 661